In general, different forms of wavelength division multiplexing (WDM) passive optical networks (PONs) face dilemmas with deploying networks utilizing cost effective optical network termination units (ONTs). Fiber optic cabling, termination units and related hardware are expensive and require significant amounts of precision tuning in order to maintain optimal performance.
The ONT, in general, must be configured to operate at a specific wavelength or wavelength group based on a random assignment from the central office equipment. The wavelength assignment scheme may be performed by an optical line terminal (OLT), which assigns the same wavelength to more than one ONT. Alternatively, the assignment scheme may assign one wavelength or a set of wavelengths to a particular group of users, which, in turn, are utilized by a corresponding group of ONTs. PONs require constant configuration and reconfiguration for wide-scale deployment. There is an ongoing challenge to produce color-less laser transmitters in the ONTs of the PONs that are cost effective, while providing flexibility with the wavelength tuning, assignment and adjustment procedure.
When implementing wavelength division multiplexing (WDM) wavelength assignments, the implementation must be planned to accommodate a large number of ONTs. WDM PON systems may not require a single wavelength per end user in the downstream and upstream directions. Within the user access environment, it is necessary to accommodate continuously growing user bandwidth requirements while maintaining a reasonable cost basis.